Systems adapted for the protection of property including devices which may be activated at one location to provide a signal either of an unauthorized entry to a premises of the unauthorized displacement of an article within the premises at another location are known in the prior art. Representative of such systems are those which are illustrated and described in U.S. Pat. Nos. 3,247,502 to Eberts, 3,487,404 to Midkiff, 3,544,987 to McMann, Jr. et al. and 3,750,131 to Fletcher et al.
Briefly, the Eberts patent signals the displacement of an article by a pair of reed switches which are closed to provide a signal if there is a break in a flux path between a permanent magnet and an armature carried by the reed. In both Midkiff and McMann, Jr. et al. a switch between relatively movable parts of an access opening to a premises is actuated to provide a signal at a remote location. In the latter, the switch is operated by a change in flux caused by movement of a magnet relative to a reed switch. In Fletcher, a signal is generated at a remote location in response to the transmission and pick-up of an inaudible transmission from a hand-held instrument.
These systems all suffer from certain disadvantages, namely the first three all require connector leads which communicate from a power source to the location of the device which shall signal the unauthorized entry or unauthorized displacement. Therefore, whether or not the device is hidden from view, the connector leads most likely will be visible to intruders thereby to provide the opportunity to disable the system. Fletcher et al. suffers from a further disadvantage, namely that the system is not one which operates unattended but rather requires the use of a hand-held device which is operated by an individual. Therefore, if the need arises to transmit a signal, the sender may not receive assistance in time to remedy the situation which precipitated resort to use of the system.